1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrostatic copying machine, an electrostatic printer and the like.
2. Related Background Art
In conventional image forming apparatuses in which a toner image is formed by applying developer to an electrostatic latent image formed on a surface of an image bearing member and the toner image is electrostatically transferred onto a transfer sheet and then the transfer sheet is heated and pressurized to fix the toner image to the transfer sheet, since it is difficult to transfer the entire developer on the image bearing member onto the transfer sheet during the transferring operation, small amount of developer always remains on the image bearing member.
Thus, in order to obtain a good quality image, residual toner (developer) remaining on the image bearing member must be removed adequately. Various means for removing the residual toner have been proposed. Among them, since an arrangement in which a sharp edge of a blade made of elastic material such as rubber is urged against the surface of the image bearing member to scrape the residual toner has a simple construction and cheap and has excellent toner removing ability, such an arrangement has widely been used.
FIG. 5 shows a typical example of such a cleaning device for an image forming apparatus. In this example, a cleaning device including a housing 9 having an opening direction toward an image bearing member is disposed in parallel with the image bearing member having an axis perpendicular to the plane of FIG. 5 and rotated in a direction shown by the arrow.
Residual toner not contributing to the transferring and remaining on the image bearing member at a lower side transfer section (not shown) is advanced to a cleaning blade 9B as cleaning means, where the residual toner is scraped by the cleaning blade. The scraped toner is carried to a conveying screw 9D through a magnet roller 9E, a doctor roller 9F and the like and then is discharged and collected. Here, since magnetic toner is used, the toner is magnetically attracted onto the magnet roller 9E.
In such a cleaning device, when the device is used for a long term, the toner particles are gradually accumulated at a contact area between the blade edge and the image bearing member, thereby reducing the cleaning ability.
It is considered that adhesion and aggregation of toner onto the blade edge is caused by lateral shifting of toner, electrostatic coherence of toner to the blade edge and/or combination thereof. Further, products such as fine powder, rosin and talc generated from the transfer sheet comprised of plain paper, and various substances such as nitride and dust caused by the presence of high voltage members such as a corona charger within the apparatus are shifted and aggregated on the blade edge together with the toner.
If such a condition occurs, the aggregated or cohered toner may be passed through the blade edge to push the blade edge upwardly thereby to worsen the cleaning ability, or the surface of the image bearing member may be abraded or the blade edge may be damaged by the foreign matters included in the residual toner.
To avoid this, while various attemptsxe2x80x94for example, the blade edge is configured to make accumulation of toner difficult or the cleaning blade is vibrated to drop the accumulated mattersxe2x80x94have been made, satisfactory results have not yet been obtained.
Further, due to the presence of additives added to the toner, the developer is partially aggregated electrostatically by to enter between the blade edge and the image bearing member or is totally aggregated electrostatically along the blade edge to push the blade edge upwardly, with the result that developer blank of 10 cm at the maximum such as streaklike blank in the former case or bandlike blank in the latter case may occur.
An object of the present invention is to provide an image forming apparatus in which developer is prevented from passing through cleaning means.
Another object of the present invention is to provide an image forming apparatus in which image blank such as streaklike blank or bandlike blank is prevented.
A further object of the present invention is to provide an image forming apparatus in which developer accumulated in cleaning means is electrostatically aggregated or cohered.
The other objects and features of the present invention will be apparent from the following detailed explanation of invention referring to the accompanying drawings.